Study On The Law And Stability Of Water Migration In Loess Cave Dwellings Under Rainfall

Loess cave dwellings,as an architectural form with national characteristics in the Loess Plateau region,not only represent the long history and culture of our country,but also carry the yearning of hundreds of millions of working people for a better life.However,due to the special water sensitivity of loess,cave dwellings in loess are very susceptible to rainfall under natural conditions.In particular,water migration caused by rainfall infiltration makes the water content of cave dwellings continuously increase,and the shear strength gradually decreases.,Which has a serious impact on the stability of loess cave dwellings.Therefore,conducting research on the law of water migration and stability of loess cave dwellings under rainfall can not only provide a theoretical basis for the stability analysis of cave dwellings under rainfall infiltration,but also has important practical significance for protecting the lives and property of residents in the Loess Plateau.This paper takes loess cave dwellings in Yan’an area of northern Shaanxi as the research object,and uses a combination of indoor tests,theoretical analysis and numerical calculations to carry out soil-water characteristic curve tests,unsaturated soil humidification deformation characteristics tests,and unsaturated soil strength tests.Unsaturated soil seepage-stress coupling model,to study the law of water migration,deformation characteristics and stability of loess cave dwellings under the action of rainfall.The main research content and conclusions of this article are as follows:(1)The pressure plate instrument was used to carry out the whole process of soil-water characteristic curve test,and the soil-water characteristic curves of Yan’an loess in the dehumidification stage and the moisture absorption stage were obtained.The difference between the dehumidification curve and the moisture absorption curve was analyzed,and the volumetric water content of the unsaturated loess was obtained.Relationship with matrix suction.Tests show that there is no one-to-one relationship between volumetric water content and matrix suction,and there is an obvious "hysteresis effect" between the moisture absorption curve and the dehumidification curve.Through the fitting analysis of the test data,it is found that the Van Genuchten model can well characterize the soil-water characteristics of Yan’an loess.(2)The stress-strain type unsaturated soil triaxial instrument was used to carry out the humidification deformation characteristics test of loess.The change curve of void ratio and volumetric water content with matrix suction under different net stresses was obtained,and the void ratio and volumetric water content and net stress sum were established.The relationship between the matrix suction and the fitting surface of Yan’an loess porosity ratio-net stress-matrix suction and the fitting surface of volumetric water content-net stress-matrix suction are obtained respectively.(3)GDS unsaturated soil triaxial instrument was used to carry out the strength test,and the stress-strain curves under different net stress and matrix suction were obtained,and the influence of net stress and matrix suction on the shear strength of unsaturated loess was analyzed.The results show that the shear strength of unsaturated loess gradually increases with the increase of net stress and matrix suction;matrix suction has a greater influence on the cohesive force of loess,but has a smaller effect on the effective internal friction angle.Through the fitting analysis of the test data,the functional relationship between the cohesion of the test loess and the suction of the matrix is established.(4)Based on the non-linear elastic constitutive relationship of unsaturated soil,combined with the obtained void ratio and volumetric water content,net stress and matrix suction,the relationship between elastic modulus and bulk modulus and net stress and matrix suction is deduced;through analysis The coupling mechanism between soil seepage and stress in the process of rainfall infiltration,based on the force balance equation and the continuity equation of the liquid phase as the basic framework,combined with the constitutive relationship of the humidification deformation characteristics,constructs the unsaturated soil seepage-stress Coupling model.(5)Based on the unsaturated soil seepage-stress coupling model,the multiphysics coupling analysis software COMSOL Multiphysics is used to analyze the water migration and deformation characteristics of loess cave dwellings under typical rainfall conditions,and discuss different rainfall intensities,different rainfall patterns,and different rainfall infiltration directions Influence on the law of water migration and stability of loess cave dwellings.Studies have shown that under typical rainfall conditions,as the rainfall continues,the infiltration depth gradually increases,the water content of the soil continues to increase,and the deformation continues to increase;the law of water migration and stability of loess cave dwellings are affected by rainfall.The influence of rainfall intensity,rainfall pattern and rainfall infiltration direction.With the increase of rainfall intensity,the improvement of rainfall pattern and the increase of rainfall infiltration inclination angle will cause the water content of the cave dwelling soil to continuously increase,and the matrix suction will continue to decrease,which makes the soil The elastic modulus of the body continues to decrease and the deformation continues to increase,which in turn leads to the continuous reduction of the safety factor of the loess cave dwellings.